A strategy for direct alkynylation of electron-deficient octafluorotoluene via selective C–F bond cleavage is exhibited. The synthesized products are super intermediates for further transformations. Additionally, we give a preliminary explanation of the mechanism for the reaction of terminal alkynes with octafluorotoluene using density functional theory (DFT).

A rhodium-catalyzed [6 + 2] cycloaddition of internal alkynes with cycloheptatriene is described. A series of substituted alkynes were cycloadded to cycloheptatriene through a [6 + 2] addition to give a variety of substituted bicyclic compounds in excellent yields. The optimal catalytic system for these transformations was a [Rh(COD)Cl]2 (5.0 mol %) catalyst in combination with CuI (10 mol %) and PPh3 (10 mol %). The proposed mechanism for this system includes an initial oxidative coupling reaction between the coordinated cycloheptatriene and the internal alkyne, followed by a [1,3]-shift of the Rh metal center and a reductive elimination from the Rh(III)–allyl complex to give the final product. Calculations using a model Rh(I) catalyst were also carried out to further understand this mechanism.

The reactions of the 16-electron half-sandwich complex CpCo(S2C2B10H10) (1) (Cp: cyclopentadienyl) with sulfonyl azides (p-toluenesulfonyl azide, TsN3; methanesulfonyl azide, MsN3) in refluxing dichloromethane or at ambient temperature lead to imido-bridged adducts CpCo(S2C2B10H10) (NSO2R) (2a, R = 4-MePh; 2b, R = Me) which can convert to the tetraazadiene cobalt complexes CpCoN4(SO2R)2 (3a, R = 4-MePh; 3b, R = Me) in the presence of excess azide if heated. The reactions of 1 with acyl azides (methyl azidoformate and benzoyl azide) lead to CpCo(S2C2B10H10)(CONR) (4a, R = OMe; 4b, R = Ph) with a newly-generated five-membered metallacyclic ring Co–S–N–C–O. Complexes 2a and 2b show further reactivity toward alkynes to give rise to the insertion products CpCo(S2C2B10H10)(R1C═CR2) (NSO2R) (R1 = COOMe, R2 = H, R = 4-MePh, 5a, R = Me, 5b; R1 = R2 = COOMe, R = 4-MePh, 6a, R = Me, 6b; R1 = COOMe, R2 = Ph, R = 4-MePh, 8a, R = Me, 8b) formed by alkyne addition to a Co–S bond to generate a Co–C–C–S four-membered ring and CpCo(S2C2B10H10)(R1C═CR2NSO2R) (R1 = H, R2 = Ph, R = 4-MePh, 7a, R = Me, 7b; R1 = COOMe, R2 = Ph, R = 4-MePh, 9a, R = Me, 9b) formed by alkyne insertion into a Co–N bond to generate a Co–C–C–N–S five-membered ring. In the case of PhC≡CCO2Me, the products with insertion into both Co–S and Co–N bonds are isolated. Interestingly, if tert-butylacetylene is used, CpCo(S2C2B10H10)(R1R2C═CNSO2R) (R1 = tBu, R2 = H, R = 4-MePh, 10a, R = Me, 10b) are generated by insertion of terminal carbon into a Co–N bond to form four-membered ring Co–C–N–S. The insertion pathways of these reactions have been discussed on the basis of DFT calculations. All the new complexes were fully characterized, and X-ray structural analyses were performed for 2a, 3a, 3b, 4a, 4b, 5a, 6a, 7a, 7b, 8a, 9a, 9b, and 10b.

Detailed mechanisms of the diboration of the acyclic α,β-unsaturated carbonyl compounds acrolein, methyl acrylate, and dimethyl fumarate (DMFU) catalyzed by Pt(0) complexes were studied with the aid of density functional theory by calculating the relevant intermediates and transition states. For acrolein and methyl acrylate, the results show that the catalyzed diboration occurs via oxidative addition of the diboron reagent to the Pt(0) complex having diimine and acrolein (or methyl acrylate) as the ligands, 1,4-conjugate addition of a Pt–B bond to acrolein/methyl acrylate to give an O-bound boron enolate intermediate containing a Pt–C–C═C–O–B linkage, and subsequent acrolein/methyl acrylate coordination to the Pt(II) center followed by reductive elimination to obtain the 1,4-diboration product of acrolein/methyl acrylate, i.e., the β-boryl-substituted O-bound boron enolate. For acrolein, the 1,4-diboration product is the final product, whereas for methyl acrylate, the 1,4-diboration product then isomerizes to the experimentally observed and thermodynamically favored 3,4-addition product, i.e., the β-boryl-substituted C-bound boron enolate, via a 1,3-shift of the O-bonded boryl group. Slightly different from what we have seen in the catalyzed diboration of acrolein/methyl acrylate, the catalyzed diboration of DMFU takes place through oxidative addition of the diboron reagent to the Pt(0) complex having DMFU and diimine as the ligands, 1,6-conjugate addition of both of the two Pt–B bonds to the coordinated DMFU ligand to give a 1,6-addition intermediate containing BegO–C(OMe)═C–C═C(OMe)–OBeg (eg = ethyleneglycolato = −OCH2CH2O−) as a ligand, and then isomerization via two consecutive 1,3-shifts of the two O-bonded boryl groups to produce the experimentally observed 3,4-diborated diastereomeric products.